THE ARCH^AX FORMATIOX OF THE ABUKUMA PLATEAU. 93 ^ 



Dr. A. Saner and Dr. i^. V. Fssing, while stndying the minerals 

 of a pegmatite dyke, have fonnd ont, that tlie microcline occnrs 

 in simple crystals, or in twin- of tlie lîas^eno type, exactly like an 

 orthoclase-crystal ; and that characteristic, cross-liatching strnrtnre, 

 by which alone the microcline- nature is nsually recognized under 

 the microscope, is not always fully deyelopcd. 'l'he true nature (^f it 

 has been ])laced l:)y l)()th authors 1:)eyond all doubt by an exact 

 chemir'al analysis, and by optical inyestigations on the well-oriented 

 ])rcparations. Tlierefore our feldspar, which is also not rloiibl\- 

 twinned, may perhaps be looked upon as a variety of microcline. 



The granite Idtberto described tbrms a wild creek along the dee|) 

 rayine of the Xatsui-gawa, which runs at its L^wer course by the 

 ]io])ulous town of Taira. Recently a new road was opened toward 

 ^[iharu, and the traffic thereby very much facilitated ; but just a 

 few years ago, it was one'of the worst roads of tliis region ; hence tlie 

 name of the Jigoku-döri, or the Deyil's way. Xew road-cuttinu-s 

 now giye good exposures of the granite. 



At various localities the hornblende-granite f)rms a gradual 

 transition to the so-called (jranite-fiiiris:^ ov <in('is.<;-fjmnili'. and we can 

 trace them step by ste]) from one extreme to the oflier, without find- 

 iiig any alnaipr discoutiiuiity. There are, howeyer, other (ineisses 

 occurring in the same region, whicli look, at first sight, like 

 schistose varieties of the preceding granite; but in truth the f uaner has 

 nothing in ct^mmon with the latter, in regard to its genesis. The 

 genuine gneisses, already referred to, are true members of the 

 arcbœan group, [lerhaps the lowest and therefore tlie oldest rocks which 

 we shall ever be able to find in tlie edifice of the fFaparjese 

 islands. Gord'usion of the genuine gneisses witli the apparent ones 

 bus thrown many of us into an intricate labyrinth, from which 



